Six pairs of arteries in vertebrate embryos, which connect the ventral aorta to the dorsal aorta by running between the gill slits. The arches are numbered I to VI from the anterior end. In adult tetrapods arches I and II are lost, III gives rise to the carotid arteries, IV (one side of which is lost in birds and mammals) becomes the systemic arch supplying the trunk and limbs, V is lost (see ductus arteriosus), and VI gives rise to the pulmonary arch supplying the lungs (see pulmonary artery). In adult fish four to six arches persist as branchial arteries supplying the gills.